1. Technical Field
The invention relates to an electrostatic image developing toner, an invisible information toner, an electrostatic image developer, a process cartridge and an image formation apparatus.
2. Related Art
Methods such as an electrophotographic method, used to form image information through an electrostatic image, are utilized in various fields. In the electrophotographic method, an electrostatic latent image is formed on an image support in a charge and exposure processes (latent image formation process) and an electrostatic latent image is developed using an electrostatic image developer (hereinafter, simply called “developer” depending on the situation) containing an electrostatic image developing toner (hereinafter, simply called “toner” depending on the situation), followed by a transfer process and a fixing process to make the image visible. The developer used here includes a two-component developer including a toner and a carrier, and a one-component developer using a magnetic toner or a nonmagnetic toner singly. As a conventional method of producing the toner, the kneading milling method is used in which a binder resin such as a thermoplastic resin is melted and kneaded together with a colorant such as a pigment, a charge control agent, a releasing agent such as wax and the like, and the resulting mixture is cooled, milled and further classified. The toner particles obtained in this manner are sometimes treated according to the requirements by adding inorganic or organic particles to the surface of these toner particles to improve the fluidity and cleaning ability of these toner particles.
Also, as the method of producing an electrostatic image developing toner, various chemical toner production methods have been developed and put to practical use which are typified by a suspension polymerization method and dissolution suspension method including an emulsion polymerization coagulating method to produce a toner. In, for example, the emulsion polymerization coagulating method, a dispersion solution of a resin formed by emulsion-polymerizing a polymerizable monomer of a binder resin and a particle dispersion solution of a colorant, releasing agent and the like are mixed with stirring in an aqueous solvent in the presence of a surfactant to coagulate and thermally fuse, thereby producing color resin particles, which are a toner having a specified particle diameter, grain size, shape and structure.
In recent years, the color electrophotographic method has spread significantly, and the fields in which this method is used have been widened with the spread of the color photographic method. Examples of these fields include a field of invisible information toners (invisible toners) used for the copyright protection of digital works such as stationary images, and prevention of illegal copying and utilized for ID cards and the like by embedding addition data recording additional information in an image in a superimposed manner, to prevent forgery and to improve security.
Particularly, the recent development of copy machine printers has made it easy to duplicate paper money, a copy of one's family resister, a written contract and the like, giving rise to problems concerning illegal copying and illegal uses.
The invisible information toner to be used for the purpose of preventing such illegal copying and the like means a toner which has almost no absorption in the visible wavelength region though it has absorption in the ultraviolet wavelength region or near-infrared wavelength region, and makes it possible to read information by any ultraviolet light or near-infrared light. For this, a bar code and an any code are imaged using the toner to embed personal or company information, voice information, or the like and the embedded information can be read by a scanner or the like.
Such an invisible information toner is characterized by the feature that it has no absorption (or almost no absorption) in the visible wavelength region and has strong absorption at an any wavelength in the near-infrared wavelength region. Here, in order for a toner to be increased in the absorption of light in the near-infrared wavelength region for the purpose of, for example, improving image-reading precision, some conventional methods are being adopted which include a method in which a large amount of near-infrared ray absorbing agent is added to the toner and a method in which the particle diameter of a near-infrared ray absorbing agent in the toner is decreased.